package com.whacos.common.utils;

/**
 * IdUtils id 生成工具类
 */
public class IdUtils {

    private final long workerId;
    private final static long twepoch = 1288834974657L;
    private long sequence = 0L;
    private final static long workerIdBits = 4L;
    private final static long maxWorkerId = -1L ^ -1L << workerIdBits;
    private final static long sequenceBits = 10L;
    private final static long workerIdShift = sequenceBits;
    private final static long timestampLeftShift = sequenceBits + workerIdBits;
    private final static long sequenceMask = -1L ^ -1L << sequenceBits;
    private long lastTimestamp = -1L;

    private static IdUtils idUtils;

    public static synchronized IdUtils getInstance() {
        if (idUtils == null) {
            idUtils = new IdUtils(2L);
        }
        return idUtils;
    }

    private IdUtils(final long workerId) {
        super();
        if (workerId > this.maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0",
                    this.maxWorkerId));
        }
        this.workerId = workerId;
    }

    private IdUtils() {
        super();
        this.workerId = 2L;
    }

    /**
     * 生成唯一id
     */
    public synchronized long nextId() {
        long timestamp = this.timeGen();
        if (this.lastTimestamp == timestamp) {
            this.sequence = (this.sequence + 1) & this.sequenceMask;
            if (this.sequence == 0) {
                timestamp = this.tilNextMillis(this.lastTimestamp);
            }
        } else {
            this.sequence = 0;
        }
        if (timestamp < this.lastTimestamp) {
            try {
                throw new Exception(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
                        this.lastTimestamp - timestamp));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        this.lastTimestamp = timestamp;
        long nextId = ((timestamp - twepoch << timestampLeftShift))
                | (this.workerId << this.workerIdShift) | (this.sequence);
        return nextId;
    }

    /**
     * 时间戳ID
     *
     * @param lastTimestamp 时间戳
     *
     */
    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    /**
     * 时间ID 生成
     *
     */
    private long timeGen() {
        return System.currentTimeMillis();
    }

    /**
     * 获取Id -- long 类型
     */
    public static long getId() {
        return IdUtils.getInstance().nextId();
    }

    /**
     * 获取id -- String 类型
     */
    public static String getIdStr() {
        return IdUtils.getInstance().nextId() + "";
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000000; i++) {
            System.out.println(getId());
        }
        System.out.println(System.currentTimeMillis() - start);
    }
}
